SUBORDER B 



TOXODONTIA 



235 



very strong symphysis, broad coronoid process and high, transverse condyle. 

 The dentition is frequently complete, highly specialised, and teeth often in 

 compact series. The incisors are often spade-like, entirely or partially covered 

 with enamel, and all or in part with closed roots. In some forms they may be 

 very much elongated, rodent-like, open below and having enamel front and 

 back or only on the front surface. P and I^ are very strongly developed. 

 All of the upper teeth from the third incisor on, and all of the lower teeth 

 from the canine on, gradually intergrade (Fig. 318). Of the four premolars, 

 the two anterior ones may be reduced and the two posterior ones become 

 molariform. The upper molars have an oblique quadrangular or triangular 

 outline, and usually a parastyle. They are made up of anectoloph and two 

 unequally developed ridges, between which there is a deep transverse valley 

 where there are one or two small crests. On the posterior surface often 

 another ridge is formed. By continued grinding, all of these prominences are 

 worn down until the valleys appear as islands, and these later also become 



Fig. 318. 



Adinotherium sp. Upper Miocene (Santa Cruz beds), Patagonia. A, Upper premolar from inside. B, C, 

 Upper molar from inside and from behind. D, Lower molar from outside. E, Lower molar from inside and 

 above. 2/g. 



worn down either completely or in part. In the primitive forms the crowns 

 are entirely covered by enamel ; among higher types the cheek teeth become 

 prismatic, the roots disappear, and enamel is restricted to the outer and anterior 

 sides or to the outer and inner sides. Often there is a cement covering which 

 surrounds the tooth either entirely or in part. The lower cheek teeth consist 

 of a short anterior and a much longer posterior crescent, besides two inner 

 pillars, the anterior of which fuses with the hinder end of the first crescent, 

 and the base of the posterior pillar fuses with the anterior end of the second 

 crescent. The prominences of the inner side are worn down by grinding to 

 form a sort of endoloph. The original valleys of these teeth also become 

 enamel islands. The upper incisors and molars are very strongly curved 

 inwardly, the lower ones forwardly. The third molar is elongated in both 

 jaws. The posterior milk-teeth resemble, on the whole, the molars, but 

 always have short, separate roots. 



The skeleton of the Toxodontia is very similar to that of the Typotheres 

 and combines many primitive characteristics with high specialisation. The 

 large scapula is similar to that of the rhinoceros, only having a rudimentary 

 acromion, which indicates that no clavicle is present. The short, strong 



